An electro photographic image forming apparatus has been known. The image forming apparatus heats a toner, which is a colorant, at a predetermined temperature (hereinafter, referred to as a fixing temperature) to fix an image of the toner on a recording medium (for example, a sheet). The image forming apparatus forms an image by the fixing operation. The image forming apparatus includes a fixing unit that fixes an image of the toner on the recording medium. The image forming apparatus has a warming-up mode, a standby mode, and a printing mode, as operation modes. The image forming apparatus controls a temperature of the fixing unit according to each operation mode. The warming-up mode is an operation mode when the image forming apparatus is powered on. The image forming apparatus in the warming-up mode controls the temperature of the fixing unit to raise the temperature of the fixing unit to a predetermined target temperature. The target temperature of the warming-up mode is, for example, a temperature close to the fixing temperature. The standby mode is an operation mode when an image forming operation is not performed after the fixing unit reaches the target temperature. The image forming apparatus in the standby mode controls the temperature of the fixing unit to keep the temperature of the fixing unit at a standby temperature. The standby temperature is, for example, the same temperature as the target temperature. The printing mode is an operation mode when the image forming apparatus is forming an image. The image forming apparatus in the printing mode controls the temperature of the fixing unit to raise the temperature of the fixing unit from the standby temperature to the fixing temperature and to keep the temperature of the fixing unit at the fixing temperature.
As the image forming apparatus, an image forming apparatus using a plurality of toners is known. For example, a color image forming apparatus is provided with four colors (black K/cyan C/magenta M/yellow Y) of toners. The color image forming apparatus forms a color image using four colors of toners. The fixing unit heats four colors of toners at the fixing temperature to fix the image of the toners on the recording medium (for example, a sheet). Fixing temperature characteristics of the toners are different according to kinds of toners. Accordingly, the temperatures necessary for fixing of the toners are different according to kinds of toners. However, the fixing temperature of the color image forming apparatus may be changed by an environmental temperature, but is not changed by kinds of toners to be used. The target temperature of the warming-up mode and the standby temperature of the standby mode in the color image forming apparatus are also not changed by kinds of toners. The reason why the fixing temperature is not changed is that four colors of toners are simultaneously fixing targets in a case of color image formation.
Meanwhile, as the image forming apparatus using the plurality of toners, an image forming apparatus provided with two kinds of toners, that is, a color erasable toner (hereinafter, referred to as an erasable toner) and a color inerasable toner is proposed. In a case of the image forming apparatus, since an image is formed using any one toner, two kinds of toners are not simultaneously the fixing targets. Accordingly, the image forming apparatus changes the fixing temperature of the fixing unit according to the kind of toner to be used. In this case, to achieve image formation using any toner between two kinds of toners, the image forming apparatus sets the target temperature (=the standby temperature) of the warming-up mode to the higher fixing temperature of the fixing temperatures of two kinds of toners.
However, in a case of forming an image using a toner with a low fixing temperature (for example, an erasable toner), since the fixing temperature of the erasable toner is lower than the standby temperature, the image forming apparatus has to lower the temperature of the fixing unit from the standby temperature to the fixing temperature of the erasable toner. A conventional fixing unit has a configuration for heating but does not have a configuration only for cooling. For this reason, generally, a time necessary to lower the temperature of the fixing unit is longer than a time necessary to raise the temperature of the fixing unit. Accordingly, the image forming apparatus provided with the erasable toner and a normal toner imposes an unnecessary standby time on the user when an image is formed using the toner with the low fixing temperature.